The present invention relates to an intermittent drive mechanism, a sheet feeder, and an image forming apparatus.
JP-A-9-236163 discloses a conventional, intermittent drive mechanism. The intermittent drive mechanism is provided on, for example, a sheet feeder provided on an image forming apparatus.
More specifically, the intermittent drive mechanism comprises a drive gear, a fragmental gear, and a first cam, which rotates integrally with the fragmental gear. The fragmental gear includes a mesh portion, whose teeth arranged in a predetermined region on a circumference mesh with the drive gear, and a non-mesh portion, which is free of teeth in the remaining region on the circumference and so does not mesh with the drive gear.
Also, the intermittent drive mechanism comprises a bias spring, an operating arm, and an operating-arm drive mechanism, which drives the operating arm upon energization of a solenoid. The bias spring contacts with the first cam to rotate the fragmental gear so as to bring about a mesh state, in which the mesh portion meshes with the drive gear, from an optional, initial position in a non-mesh state, in which the non-mesh portion faces the drive gear. The operating arm engages with the fragmental gear to restrict rotation of the fragmental gear only when the fragmental gear is disposed in the initial position.
The conventional intermittent drive mechanism constructed in this manner can drive the fragmental gear intermittently in the following manner.
First, in a state, in which the fragmental gear stops in the initial position, the operating-arm drive mechanism does not carry an electric current to the solenoid and the operating arm engages with the fragmental gear to restrict rotation of the fragmental gear. At this time, the bias spring contacts with the first cam while conserving a bias force.
Subsequently, when intermittent driving of the fragmental gear starts, the operating-arm drive mechanism carries an electric current to the solenoid to drive the operating arm. Therefore, the operating arm does not engage with the fragmental gear and so rotation of the fragmental gear is not restricted. Therefore, the bias spring biases the first cam whereby the fragmental gear rotates and the fragmental gear is put in a mesh state. Consequently, the driving force of the drive gear is transmitted to the fragmental gear, so that the fragmental gear rotates.
Further, when the fragmental gear rotates to be again put in a non-mesh state, the driving force of the drive gear is not transmitted to the fragmental gear. Therefore, the fragmental gear rotates to the initial position due to inertia and the bias on the first cam by the bias spring. Here, since the operating-arm drive mechanism does not carry an electric current to the solenoid except at the start of intermittent driving, the operating arm engages again with the fragmental gear. Consequently, the operating arm restricts rotation of the fragmental gear and so the fragmental gear remains in the initial position.
Thus the conventional intermittent drive mechanism enables intermittent driving of the fragmental gear. The intermittent drive mechanism is provided on, for example, a sheet feeder to drive a sheet feed gear directly or indirectly, thus enabling intermittently rotating a pickup roller, which is driven by the sheet feed gear. Therefore, an image forming apparatus provided with such sheet feeder can form an image on sheets fed one by one by the pickup roller, or the like.
By the way, noise reduction at the time of sheet feed is demanded of image forming apparatuses and sheet feeders in order to achieve a decrease in discomfort on the part of a user, and noise reduction is also demanded of the conventional intermittent drive mechanisms.